Lubricants



United States Patent LUBRICANTS 1 Ellis K. Fields, Chicago, m., and Clyde s. Scanley, Ogden Dunes, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application November 25, 1952, Serial No. 322,572

Claims. (Cl. 252-32.7)

lems in the lubrication of the'modern internal combus tion engine. To meet the increased severe demands upon engine lubricants, many types of lubricant additives have been developed to obtain certain .desired characteristics thereof. Among the more effective addition agents which have been developed for compounding with lubricants are many sulfur-containing organic compounds, such as ice 1 eral formula:

phatic, aryl and alkaryl radicals of from 2 to about or more carbon atoms. Examples of suitable hydrocarbon radicals are butyl, hexyl, octyl, nonyl, decyl, dodecyl, tridecyl, hexadecyl, octadecyl, benzyl, butylphenyl, etc., radicals; R and R can be the same or different radicals. These esters are readily prepared by reacting 2,5-dimercapto-1,3,4-thiadiazole with an organic acid chloride in the molar ratio of 1:2 at a temperature of from about 25 C. to about 130 C. for one-half to twenty hours. To facilitate the reaction, suitable solvents, for example, benzene or dioXane, can be used. The reaction product is freed of hydrogen chloride and any carboxylic acid by washing with a dilute aqueous alkali solution or by passing a benzene solution of the reaction products through a column of activated alumina.

Examples of carboxylic esters of 2,5-dimercapto:l,3,4- thiadiazole are:

Dilauroylester of 2,5-dimercapto-1,3,4-thiadiazole Distearoyl ester of 2,5-dimercapto-1,3,4-thiadiazole by way of example, sulfurized terpenes, sulfurized hydro- I carbonoil's, vegetable oils or animal oils, xanthate esters, organic polysulfides, particularly polyalkyl .polysulfides, metal salts of organo-substituted thioacids of phosphorus, metal salts of the reaction products of a phosphorus sulfide and a hydrocarbon, such as for example, polybutenes and other polyolefins, and combinations of the foregoing.

Recent increased use of silver and similar metals in the construction of improved internal combustion engines has created new problems in the use of sulfur-containing additives in lubricants for such engines; the primary problem created being the corrosion of such silver partsof the engine by the sulfur-containing additives. While such corrosion can be eliminated by avoiding the use of sulfurcontaining additives in lubricants for such engines, this solution of the problem is accompanied by the loss of the highly desired beneficial effects of the additives of this type.

It is an object of the, present invention to provide a non-corrosive composition. 'Another object of the invention is to provide a composition non-corrosive to silver and similar metal. A still further object of the invention is to provide a composition which will inhibit the corrosion of silver and similar metal by sulfur and/or organo sulfur-containing compounds. A still further object of the invention is to provide a lubricant composition which is non-corrosive.

Still another object of the invention is to provide a lubricant composition containing an addition agent which will inhibit the corrosion of silver and.

similar'metal by sulfur and/ or organo sulfur-containing compounds. A further object of the invention is to provide a method of inhibiting the corrosion of silverand Dibehenoylester of '2,5-dimercapto-1,3,4-thiadiazole Diarachidoyl ester of 2,5-dil'nercapto-1,3,4-thiadiazole Dic'aproyl ester of 2,5 -dimercapto- 1,3 ,4 -thiadiazole Lauroyl butyroyl ester of 2,5 dimercapto-1,3,4-thiadiazole Ditridecoyl ester of 2,5-dimercapto-l,3,4-thiadiazole Lauroyl stearoyl ester of 2,5-dirnercapto-1,3,4-thiadiazole Di-p-t-butyl benzoyl ester of 2,5-dimercapto-1,3,4-thiadiazole I The preparation of theherein-described esters is illus trated by the following examples:

EXAMPLE I A mixture of 87.2 grams (0.4 mole) lauroyl chloride, 30 grams (0.2 m.) 2,5-dimercapto-l,3,4-thiadiazole, and 50 cubic centimeters benzene was stirred and refluxed at C. for fourteen hours, at which time there was substantially no further evolution of hydrogen chloride. The product, diluted with 300 cubic centimeters of benzene, was passed through a column of activated alumina and the filtrate evaporated on the steam bath. The recovered product, 104 grams, was a light brown solid having a melting point of 68-72 C. The product was the dilauroyl ester of 2,5-dimercapto-1,3,4-thiadiazole, as indicated by the following analysis:

chloride (containing some palmitoyl and oleyl chlorides), 30 grains (.2 mole) 2,5-dimercapto-1,3,4-thiadiazole and cubic centimeters benzene was refluxed for sixteen hours. Two' hundred grams benzene were then added and the warm solution filtered through activated alumina and the diluent evaporated on a steam bath. grams of a light brown semi-solid was obtained which had a sulfur content of 12.4% and a nitrogen content of 3.52%.,

EXAMPLE III A mixture of 45 grams (.3 mole) 2,5-dimercapto-l,3,4- thiadiazole, 117.9 grams .6 mole) p-t-butyl benzoyl 3 chloride and 100 cc. toluene was stirred at 110 C. for sixteen hours. 48 cc. pyridine was added, dropwise, the mixture stirred at 95 C. for three hours, cooled and filtered, and the filtrate Stripped in vacuo. The semisolid was dissolved in ether, the ether solution filtered and evaporated, leaving a solid residue which analyzed 8.7% S and 2.91% N. v V v The esters may also be prepared by reaction of the free carboxylic acids, acid anhydrides or acid esters with the 2,S-dimercapto-l,3,4-thiadiazole. p

The above-described compounds are used in combination with lubricant base oils, such as hydrocarbon oils, synthetic hydrocarbon oils, such as those obtained by the polymerization of hydrocarbons such as olefin polymers, for example, polybutenes, polypropylene and mix tures thereof, etc., synthetic lubricating oils of the alltylene-o'xide type, for example, the Ucon oils, marketed by Carbide and Carbon Corporation, as well as other synthetic oils, such. as the polycarboxylic acid estertype oils, such as the ester of adipic acid, sebacic acid, maleic acid, azelaic acid, etc.

While the above-described products can be suitably employed alone in concentrations of from about 0.02% to about 10%, preferably from about 0.25% to about 5%, in combination with a base oil,they are usually used in combination with other lubricant addition agents, which impart various desired characteristics to the base oil. Usually, these reaction products are used in conjunction with detergent-type additives, particularly those which contain sulfur or phosphorus and sulfur. Additives of this type are usually used in amounts'of from about 0.002% to about and preferably from about 0.01% to about 5% .Among the phosphorus and sulfurcontaining addition agents are the neutralized reaction products of a phosphorus sulfide and a hydroearbo'n, an alcohol, a ketone, an amine or 'an ester." Of the phosphorus sulfide reaction product additives, we prefer 'to employ the neutralized reaction products of a phosphorus sulfide, such as a phosphorus pentasulfide, and a hydrocarbon of the type described in U. S. 2,316,082 issued to C. M. Loane et al.', April 6, 19431 As taught in this patent, the preferred hydrocarbon constituent of the reaction is a mono-olefin hydrocarbon polymer resulting from the polymerization of low molecular weight mono-olefin hydrocarbons, such as propylene, bu'tene's, amylenes, or copolymers thereof. Such polymers may be obtained by the polymerization of mono-olefins of less than 6 carbon atoms in the preseiiee of a catalyst, such as sulfuric acid, phosphoric acid, boron fluoride, aluminum chloride, or other similar halide catalysts of the FriedehCrafts type. a

The polymers employed are preferably i'iribno olefin polymers or mixtures "of mono-stem; olymers and isomono-olefin polymers having inpleeular weights ranging from about 150 to about 50,000 or more, and pref erably from about 500 to about 10,000. such polymers can be obtained, for example, by the polymerization in the liquid phase of a hydrocarbon mixture containing monoand isomono-olefins, such as butylene and 'is'obutylene at a temperature of from about '80 F. to about 100 F. in the presence of a metal halide catalyst of the Friedel-Crafts type, such as for example, boron fluoride, aluminum chloride, and the like. In the preparation of these polymers a hydrocarbon mixture containing isobutylen'e, butylenes and butanes'recovered from petroleum gases, especially those gases, produced in the cracking of petroleum oils in the manufacture of gasoline, can be used. i

Another suitable polymer -is that obtained by Epolymerizing in the liquid phase, a hydrocarbon mixture comprising substantially Ca hydrocarbons in *thepresence of an aluminum chloride-complex catalyst. The catalyst is preferably prepared by heating aluminum chloride with isooetane. The hydrocarbon mixture is introduced into the bottom of the reactor and passed upwardly through the catalyst layer, while a temperature of from about 50 F. to about 110 F. is maintained in the reactor. The propane and other saturated gases pass through the catalyst, while the propylene is polymerized under these conditions. The propylene polymer can be fractionated to any desired molecular weight, preferably from about 500 to about 1000 or higher.

Other suitable polymers are those obtained by polymerizing a hydrocarbon mixture containing about 10% to about 25% isobu'tylene at a temperature of from about 0 F. to about 100 F., and preferably 0 F. to about 32 F. in the presence of boron fluoride. After the polymerization of the isobutylene together with a relatively minor amount orthonormal olefins present, the reaction mass is neutralized, washed free of acidic substances and the unreacted hydrocarbons subsequently separated from the polymers by distillation. The polymer mixture so obtained, depending upon the temperature of reaction, varies in consistency from a light liquid to viscous oily material and contains polymers having molecular weights ranging from about 100 to about 2000, or higher. The polymers so obtained may be used as such, or, the polymer may be fractionated under reduced pressure into fractions of increasing molecular weights and suitable fractions obtained reacted with the phosphorussulfide to obtain the desired reaction products. The bottoms resulting from the fractionation of the polymer which may have Sayb o lt Universal viscosities at 210 F .ranging from about 50 seconds to about 10,000 secends, are well suited for this purpose.

. ,Essentially paraifinic hydrocarbons, such as bright stock .residuums, lubricating oil distillates, petrolaturns,

or waxes; may be used. There can also be employed the condensation products of any of the foregoing hydrocarbona usually through first halogenating the hydrocarbons with aromatic hydroearbons in thepresence or anh drous inorganic halides, such as aluminum chloride, zinc chloride, boron fluoride, 'and the like.

Examples of other high molecular-weight olefinic hydrooarboiis which can be employed are cetene (C15), ce'rotenj (C26), Tn'elehe (C30), and mixed high molecular weightalltehes obtained by cracking petroleum oils.

preferred olefins suitable for "the preparation of the phosphorus sulfide reaction products are olefins havih'g at least :20 carbon atoms in the molecule of which from about 13 "carbon atoms to about 18 carbon atoms, and prete'rablyat least 15 carbon atoms are in a long i chai'n. 'Su'ch olefins can be obtained by the dehydrogeha'tion of alkyl ha'li'des, preferably long chain alkyl halides, particularly halogenated paraffin waxes.

Asaf'st'arting material there can housed the polymer or synthetic inbrrcating oil obtained hy polymerizing unsaturated hydrocarbons resulting from the. vapor phase cracking of parafin waxes in the presence of aluminum hloride whiehis fully describ d in United States Patents Nos. 1,955,260, 1,970,402 and 2,091,398. Still another type of olefin polynrer which may be employed is the polyhr nresnliingffrom the treatment ofv'apor phase ciiaeked gasoline and/or gasoline fractions with sulfuric acid or solid adsorbents, such as Fullers earth, whereby unsaturated polymerized hydrocarbons are removed. The reaetionpioducts of the phosphorus sulfide and the olymers. resulting from the yoltolization of hydrocarbons as described "for example in United States Patents Nos. 2,197,768at1d 2,191,787 are also suitable.

Other hydrocarbons that can "be reacted with a phosphorus sulfide are aromatic hydrocarbons, such as for exampl henzeneyii phthalene, toluene, xylene, diphenyl, and the like, orw ith an 'alkylated aromatic hydrocarbon, such as for example, benzene having an alkyl sub'stituent having at least four carbon atoms, and preferably at least eight carbon atoms, such as a long chain paraffin Wax.

The phosphorus sulfide-hydrocarbon reaction product can be readily obtained by reacting a phosphorus sulfide, forexan'iple, P285, with the hydrocarbon at a temperature phosphorus sulfide can be used and separated from the product by filtration or by dilution with a hydrocarbon solvent, such as hexane, filtering and subsequently removing the solvent by suitable means, such as by distillation. If desired, the reaction product can be further treated with steam at an elevated temperature of from about.100 F. to about 600 F.

The phosphorus sulfide-hydrocarbon reaction product normally shows a titratable acidity which is neutralized by treatment with a basic reagent. The phosphorus sulfidehydrocarbon reaction product when neutralized with a basic reagent containing a metal constituent, is characterized by the presence of retention of the metal constituent of the basic reagent.

The neutralized phosphorus sulfide-hydrocarbon reaction product can be obtained by treating the acidic reaction product with a suitable basic compound, such as hydroxide, carbonate, oxide or sulfide of an alkaline earth metal or an alkali metal, such as for example, potassium hydroxide, sodium hydroxide, sodium sulfide, calcium oxide, lime, barium hydroxide, barium oxide, etc. Other basic reagents can be used, such as for example, ammonia or an alkyl or aryl-substituted ammonia, such as amines. The neutralization of the phosphorus sulfidehydrocarbon reaction product is carried out preferably in a non-oxidizing atmosphere by contacting the acidic reaction product either as such or dissolved in a suitable solvent, such as naphtha, witha' solution of'the basic agent. As an alternative method, the reaction product can be treated with solid alkaline compounds, such as KOH, NaOH, NazCOs, KzCOa, CaO, BaO, Ba(OH)2,Na2S and the like at an elevated temperature of from about 100 to about 600 F. Neutralized' reaction products containing a heavy metal constituent, such'as for example, tin, titanium, aluminum, chromium, cobalt,'zinc, iron and-the like can be obtained by reacting a salt of the'desired heavy metal with the phosphorus sulfide-hydrocarbon reaction product which has been treated with the phosphorus sulfide-hydrocarbon reaction product, which has been treated with a basic reagent, such as above described.

Other phosphorus sulfide reaction products which can be used are the reaction products of a phosphorus sulfide and a fatty acid ester of the type described in U. S. 2,399,243; the phosphorus sulfide-degras reaction products of U. S. 2,413,332; the reaction product of an alkylated phenol with the condensation product of P255 and turpentine of U. S. 2,409,877 and U. S. 2,409,878; the reaction product of a phosphorus sulfide and stearonitrile of U. S. 2,416,807, etc.

The silver corrosion-inhibiting property of the above-. 7

described carboxylic esters of 2,5-dimercapto-1,3,4-thiadiazole is demonstrated by the data in Table I, which were obtained by subjecting mixtures of hydrocarbon oils, a neutralized reaction product of P285 and a polybutene and carboxylic esters of 2,5-dimercapto-l,3,4-thiadiazole to the following test, hereinafter referred to as the modified EMD testz A silver strip 2 cm. x 5.5 cm. with a small hole at one end for suspension, is lightly abradedwith'No. steel wool, wiped free of any adhering steel wool, washed with carbon tetrachloride, air-dried and then weighed to 0.1 milligram. 300 cc. of the oil to be tested is placed in a 500 cc. lipless glass beaker, and the oil heated'to a tem-. perature of 300 F. (+2 F.) and the silver strip suspended in the oil so that the strip is completely immersed therein.

The oil in the beaker is stirred by means of a glass stirrer operating at 300 R. P. M. At the end of twenty-four hours, the silver strip is removed and while still hot rinsed thoroughly with carbon tetrachloride and air-dried. The appearance of the strip is then visually noted and given ratings according to the following scale:

1Bright 2-Stained 3--Grey-Black 4Black, Smooth 5--Black, Flake After the visual inspection the silver strip is immersed I in a 10% potassium cyanide solution at room temperature until the silver surface assumes its original bright or silver appearance. The silver strip is then washed successively with distilled water and acetone, air-dried and weighed. I

The following lubricant compositions were subjected to the above test and the results obtained tabulated in Table I Sample: Silver corrosion (wt. loss Mg) A 20-25 B 0/1 Since a weight loss of 20 milligrams is allowable, the ability of the2,5-dimercapto-1,3,4-thiadiazole derivatives of this invention to inhibit silver corrosion is demonstrated by the above data.

The effectiveness of the herein-described esters of 2,5- dirnercapto-1,3,4-thiadiazole in inhibiting corrosion of copper and/or lead-containing metals, such as for example, copper-lead alloys, is demonstrated by the data in Table II, obtained by subjecting lubricants containing the additive tothe following test:

A copper-lead test specimen is lightly abraded with steel wool, washed with naphtha, dried and Weighed to the nearest milligram. The cleaned copper-lead test specimen is suspended in a steel beaker, cleaned with a hot trisodium phosphate solution, rinsed with water, acetone and dried, and 250 grams of the oil to be tested, together with 0.625 grams lead oxide and 50 grams of 3035 mesh sand charged to the beaker. The beaker is then placed in a bath or heating block and heated to a temperature of 300 F. (:2" F.) while the contents are stirred by means of a stirrer rotating at 750 R. P. M. The contents of the beaker are maintained at this temperature for At the end of an additional twenty-four hours of test operation, the test specimen is again placed in the beaker together with an additional 0.250 gram of lead oxide and the test continued for another twenty-four hours (seventytwo hours total). At the conclusion of this time, the test specimen is removed from the beaker, rinsed in naphtha, and dried and weighed.

The loss in weight of the test specimen is recorded after each weighing.

This test, known as the sand stirring corrosion test, is referred to hereinafter as SSCT.

The data obtained when subjecting Samples A andB above, to the foregoing test, are tabulated in Table II.

fail to pass the above-described EMD test.

Since weight-losses of 200 milligrams in forty-eight hours and 500 milligrams in seventy-two hours are allowable, the copper-lead inhibiting property of the hereindescribed esters of' 2,5-dimercapto-1,3,4'thiadiazole is clearly demonstrated by the above data.

Under certain conditions, it is desirable to use in lubricant compositions from about 0.01% to about and or more'secondaryadditives -in lubricant compositions,

the invention .is not-restricted to such use since these derivatives findutility when used alone in various lubricant compositions or hydrocarbon oil compositions to impart 2 improved and desiredv characteristics thereto.

, Thus, forexample,lthese derivatives may be. used alone in hydrocarbon oils .of high sulfur crudes to inhibit the corro'sionaof. such-.oils. tosilver orcopperand/or leadcontainingmetalsu. p

:In addition to theaforementioned detergent-type additivesv and corrosion inhibitors, compositions containing the preferably 0.1% to about 2% elemental sulfur or an organic sulfur-containing compound of the type hereinabove described, either alone or in combination with,

other additives. Effective lubricant compositions are obtained by the combination of the neutralized reaction products of a phosphorus sulfide and a hydrocarbon, as above described, with elemental sulfur or anorganic su1ur-containing compound, such'as sulfurized mineral oils, sulfurized non-drying animal and vegetable oils, sulfurized olefins and olefin polymers, sulfurized sperm oil,

, etc., as described and claimed in U. S. Reissue 22,464,

issued to C. D. Kelso, et al., April 4, 1944, or withsulfurized terpenes, for example, dipentene as described and claimed in U. S. 2,422,585, issued to T. H. Rogers et 211., June 17, 1947. While these compounds impart highly desired characteristics to lubricants and effectively inhibit the corrosion of copper and/ or lead, they are under some this reason, lubricants containing such addition agents In accordance'with the present invention, however, the incorporation in such lubricant composition. of small amounts, namely from about 0.1% to about 10%, and preferably from about 0.25% to about 5% of the herein-described esters of 2,5-dimercapto-1,3,4thiadiazole etfectively inhibits the corrosiveness of the silver corrosive compounds without impairing their other desired properties.

The ability of the herein-described esters of 2,5-dimercapto-1,3,4-thiadiazole to inhibit the silver corrosion tendency of active sulfur-containing organic compounds is demonstrated by the following EMD data in Table III, obtained with the following compositions:

Sample A'.Control (solvent extracted SAE 30 oil+3.3% barium-containing neutralized reaction product of P255 and a polybutene of. about 1000 molecular weight+0.75% sulfurized dipentene).

Sample B'.A'+0.1% product of Example 1.

Sample C'.-A+0.2% product of Example 1.

Sample D.--A+0.l0% product of Example III.

Sample E.-A'+0.15% product of Example III.

Table III Sample: EMD (loss in Mg.)

A 110 B 18 C 0 D 9 E 0 As indicated by the above data, the herein-described esters of 2,5-dimercapto-1,3,4-thiadiazole effectively inhibit corrosion tendencies of active sulfur-containing organic compounds, i. e., sulfurized terpenes toward silver. However, these derivatives do not deleteriously aflect the corrosion inhibiting properties of the sulfur-containing organic compounds, such as for example, sulfurized dipentene, towards metals, such as copper and/ or lead, etc.

Although the invention has been described in connection with the use of the herein-described esters of 2,5-dimercapto1,3,4-thiadiazole in combination with the one conditions, corrosive to silver and similar metals, and for herein-described derivatives of 2,5-dimercapto-1,3,4-thiadiazolecan contain otheradditives, such as anti-oxidants, pourpointwdepressors, extreme pressure agents, anti-wear agents,.V. I. improvers, etc.:

..While this invention has been described in connection with use of the herein-described additives and lubricant compositions, theiruse is not limitcd thereto but the same can be used in productsother than lubricating oils, such as for example, .fueloils, insulating oils, greases, nondryinganimal and vegetable oils, waxes, .asphalts and any fuelsqfor internal combustion engines, particularly where sulfur corrosion must be inhibited.

Percentages given herein and in the. appended claims I are weight p ercentages unless otherwise stated. Although the present invention has been described with referencetospecific' preferred. embodiments thereof, the

invention, is notto be considered as limited thereto, but includes within its scope such modifications and variations as come withintheyspirit of theappended claims.

We'claimp,

1, Acompositioncomprising a major proportion of an oleaginous, material containing a compound, normally corrosive. to .silver, selected fromthegroup consisting of elemental; sulfur, a sulfur-containing organic compound and mixtures thereof, and fromebout 0.02% to about 15% of a carboxylicester of 2,5-dimercapto-1,3,4-thiadiazolehavingthe general formula;

in which Rand R arehydrocarbon radicals of from about 2 to about 30 carbon atoms.

2. A composition asdescribed in claim 1. in which R and R arealiphatic radicals.

3. Acompositionas described in claim 1 in which R and R are lauryl radicals.

. 4. ,A composition as described in claim 1 in which R and R are stearyl radicals.

5. A- composition as described in claim 1 in which R and R are octyl radicals.

6. A;composition as described in claim 1 in which R and R are aromatic radicals.

7. A composition as described in claim 1 in which R and R are butyl phenyl radicals.

8 A composition comprising a major proportion. of an oleaginous compound, from about 0.001% to about 10% of a sulfur-containing organic compound normally corroslve to silver, and from about 0.02% to about 15% of a carboxylic esterof 2,5-dimercapto-1,3,4-thiadiazole having the general formula:

in which R and R are hydrocarbon radicals of from about 2 to'about 30 carbon atoms.

, 9.. A composition as described in claim 8 in which the sulfur-containing organic compound is a. sulfurized terpene.

10. A lubricant composition comprising a major proportion of 'a-lubricating oil, from about 0.0001% to about 10% of a phosphorus and sulfur-containing detergent-type lubricant additive, and from about 0.02% to about 15 of a carboxylic ester of 2,5-dimercapto-1,3,4-thiadiazole having the general formula:

in which R and R are hydrocarbon radicals.

11. A lubricant composition as described in claim in which the phosphorus and sulfur-containing detergenttype lubricant additive is the neutralized reaction product of a phosphorus sulfide and a hydrocarbon.

12. A lubricant composition as described in claim 10 in which the phosphorus and sulfur-containing detergenttype lubricant additive is derived from an olefin polymer.

13. A lubricant composition as described in claim 10 in which the phosphorus and sulfur-containing detergenttype lubricant additive is a potassium-containing neutralized reaction product of a phosphorus sulfide and an olefin polymer.

14. A lubricant composition as described in claim 10 in which the phosphorus and sulfur-containing detergenttype lubricant additive is an alkaline earth-containing neutralized reaction product of a phosphorus sulfide and an olefin polymer.

15. A lubricant composition as described in claim 10 in which the phosphorus and sulfur-containing detergenttype lubricant additive is a barium-containing neutralized reaction product of a phosphorus sulfide and an olefin polymer.

16. A lubricant composition as described in claim 10, in which the phosphorus and sulfur-containing detergenttype lubricant additive is a calcium-containing neutralized reaction product of a phosphorus sulfide and an olefin polymer.

17. A lubricant composition comprising a major proporsilver, and from about 0.02% to about 15% of a carboxylic ester of 2,5-dimercapto-1,3,4-thiadiazole having the general formula:

in which R and R are hydrocarbon radicals.

18. A composition comprising a major proportion of a lubricating oil containing a compound, normally corrosive to silver, selected from elemental sulfur, a sulfur-containing organic compound and mixtures thereof and from about 0.02% to about 15% of dilauroyl ester of 2,5-dimercapto-1,3,4-thiadiazole.

19. A composition comprising a major proportion of a lubricating oil containing a compound, normally corrosive to silver, selected from elemental sulfur, a sulfur-containing organic compound and mixtures thereof and from about 0.02% to about 15 of distearoyl ester of 2,5-dimercapto-1,3,4-thiadiazole.

20. A composition comprising a major proportion of a lubricating oil containing a compound, normally corrosive to silver, selected from elemental sulfur, a sulfur-containing organic compound and mixtures thereof and from about 0.02% to about 15% of di-p-t-butyl benzoyl ester of 2,5-dimercapto-1,3,4-thiadiazole.

References Cited in the file of this patent UNITED STATES PATENTS 2,690,999 Lowe et al Oct. 15, 1954 

1. A COMPOSITION COMPRISING A MAJOR PROPORTION OF AN CLEAGINOUS MATERIAL CONTAINING A COMPOUND, NORMALLY CORROSIVE TO SILVER, SELECTED FROM THE GROUP CONSISTING OF ELEMENTAL SULFUR, A SULFUR-CONTAINING ORGANIC COMPOUND AND MIXTURES THEREOF, AND FROM ABOUT 0.02% TO ABOUT 15% OF A CARBOXYLIC ESTER OF 2.5-DIMERCAPTO-1,3,4-THIA DISAZOLE HAVING THE GENERAL FORMULA: 